1. Field of the Invention
The present invention relates to an overhead hoist transfer which transfers semiconductor wafers, etc., in a semiconductor clean room, etc., and in particular an overhead hoist transfer comprising a moving carriage having a hand portion, which holds a load, elevatably suspended therefrom, and a means for teaching an appointed stop position just above a placement base on which the above load is placed.
2. Description of the Prior Art
In, for example, a semiconductor clean room, etc., semiconductor wafers are frequently transferred between equipment to equipment, between equipment and a stocker, etc., in the production of semiconductor devices. As one of the apparatuses which transfer such semiconductor wafers, an overhead hoist transfer (hereinafter called "OHT") which causes a moving carriage, from which a load is suspended, to travel along a rail has been particularly noted. Hereinafter, a description is given of an OHT used in a general semiconductor clean room.
FIG. 5 shows a state in a semiconductor clean room in which a general OHT is installed. In a semiconductor clean room shown in the same drawing, a plurality of processing apparatuses 51 and stockers 52 are disposed, and a load port 53 (an example of a placement base) on which a wafer carrier W (an example of a load) is installed on the respective processing apparatuses 51 and stockers 52. In addition, an OHT 61 is installed in the vicinity of a ceiling, which transfers a wafer carrier W between the above processing apparatuses 51 and stockers 52.
The OHT 61 is composed of a rail 62 disposed in the vicinity of a ceiling so that the processing apparatuses 51 and the stockers 52 are connected to each other, a moving carriage 63 travelling along the rail 62, and a hand portion 65 suspended from the moving carriage 63 by a suspension member 64 (See FIG. 6). The hand portion 65 is elevated and lowered by winding and unwinding the suspension member 64 by means of a winding device (not illustrated) which is installed in the moving carriage 63.
FIG. 7 is a cross-sectional view showing the relationship in position between the rail 62, the moving carriage 63, which constitutes the OHT 61, the processing apparatuses 51, and the load port 53 of the stocker 52. As shown in the same drawing, the rail 62 is disposed so that the center position of a wafer carrier W placed on the load port 53 is made roughly coincident with the center position of the hand portion 65. However, it is difficult to strictly coincide these two center positions with each other. In fact, many cases exist where some positional deviation occurs. This is the same as regards a deviation (deviation in the stop position) in the direction along the rail 62. However, in a state where such a deviation occurs, actions of holding and placing the wafer carrier W by the hand portion 65 cannot be accurately carried out. Therefore, the moving carriage 63 is provided with a position correcting device 66 which micro-moves the suspension member 64 and hand portion 65 in the X, Y directions (two directions in the horizontal plane) and .theta. direction (rotation direction in the horizontal plane). The position correcting device 66 operates on the basis of position correcting data taught in advance for each of the processing apparatuses 51 and stockers 52.
Herein, teaching of the position correcting data is performed by accurately positioning the center position of the hand portion 65 at the center position of the wafer carrier W while actually causing the above position correcting device 66 to move by radio (or by electric waves, infrared rays, etc.) by operating a teaching box. In detail, for example, the teaching is carried out in compliance with the following procedure. Also, the position correcting data to be taught here include a moving distance (elevating distance of the hand portion 65 ) in the Z direction (the perpendicular direction) in addition to the position correcting distances in the above X, Y and .theta. directions.
(1) The moving carriage 63 is caused to stop on an appointed load port 53 by operating the teaching box. At this time, the moving carriage 63 automatically stops by, for example, reading a stop mark secured at an appointed position on the above rail 62 (At this time, it is assumed that the coordinates of the hand portion are X.sub.0, Y.sub.0, Z.sub.0, and .theta..sub.0).
(2) By operating the teaching box, the hand portion 65 is caused to move in the X, Y, Z and .theta. directions, whereby the wafer carrier W is placed on the load port 53 or is positioned at a position where the wafer carrier W is taken away from the load port 53 (the coordinates of the hand portion are assumed to be X.sub.i, Y.sub.i, Z.sub.i, and .theta. after the positioning is finished)
(3) (X.sub.i -X.sub.0, Y.sub.i -Y.sub.0, Z.sub.i -Z.sub.0, and .theta..sub.i -.theta..sub.0) are calculated. The data are used as position correcting data and stored in a memory in the moving carriage 63.
By repeating the above procedures for each of the moving carriages and load ports, the teaching of the position correcting data is carried out.
Continuously, a brief description is given of the procedures of transfer actions made by the OHT 61.
(1) An empty moving carriage 63 is caused to move the instructed processing apparatus 51 or stocker 52 (the source of transfer) and is caused to stop at an appointed stop point.
(2) The position correcting device 66 is caused to move on the basis of the position correcting data taught in advance, whereby the center position of the hand portion 65 is made coincident with the center position of the wafer carrier W on the load port 53.
(3) Lowering the hand portion 65, the wafer carrier W on the load port 53 is held. After that, the hand portion 65 is elevated.
(4) The moving carriage 63 is caused to move upward of the instructed processing apparatus 51 or stocker 52 (the target of transfer), and is caused to stop at an appointed stop point.
(5) Actuating the position correcting device 66 on the basis of the position correcting data taught in advance, the center position of the hand portion 65 is made coincident with the center position of the wafer carrier W on the load port 53.
(6) Lowering the hand portion 65, the wafer carrier W held by the hand portion 65 is placed on the load port 53. After that, the hand portion 65 is elevated.
However, since, in the above conventional OHT 61, it was necessary to teach the position correcting data to each of the load ports 53 by the hand of an operator on the basis of the above procedures, time and manpower required for the teaching work were tremendously great. For example, generally, in the case of a process (20 through 30 m long) called a "bay", since there are generally approximately 30 (or 15 through 40) units of processing apparatuses, the number of times of teaching will be as follows if it is assumed that, for example, three moving carriages are provided;
3 (quantity of moving carriages).times.30(quantity of apparatuses).times.2(Number of ports).times.2(loading and unloading) =360 times.
In addition, where it is assumed that 10 bays are provided, the number of times of teaching will be 3,600 times, wherein if it is assumed that ten minutes are required per teaching, it takes 600 hours in total in the teaching work, which is tremendously great. Moreover, one to two persons are required for the above work per moving carriage for a longer peroid of time.